There are several circadian subsystems in the body whose usual fixed phase coordination may become uncoupled. When circadian systems are uncoupled experimentally, symptoms resembling depression result, and conversely, there is some laboratory evidence of uncoupling of circadian phases in depressed patients. Pilot studies indicate manic depressives may have a fast free-running rhythm. We are exploring circadian rhythms in patients with "endogenous" affective diseases: a) unipolar depression, b) bipolar affective disease, depressed phase, and c) bipolar affective disease, manic phase. Also, control groups with d) reactive depressions and e) no affective disease are being studied. Hospitalized patients are rated at admission on a clinical symptom scale by two psychiatrists, and affect fluctuations are rated thereafter. Continuous tape-recorded activity is measured to study sleep-wakefulness cycles, and oral temperature, urinary volume, and electrolytes are also collected. Statistical analyses estimate circadian rhythm frequency, phase, and amplitude for each variable to differentiate circadian disturbances in each affective syndrome.